From a purely statistical standpoint, vaccines are a no-brainer. But everyone has this one story about something going wrong. As a scientist, and from a personal point-of-view, I can comment on this.
For three out of the last ten years, I got the flu shot. Each of those years I got the flu. The other seven years, I neither got the flu shot nor the flu. Now is it possible this is entirely a coincidence? Yes. The flu could have just been worse those three years, or I could have got lucky or unlikely, as you may.
I also understand that it is sometimes difficult to predict the exact effects of injecting genetic material into the body. This concern is why genetic-based medicines have not moved forward as fast as promised. The delivery paradigms can be challenging and require significant individual optimization of dosing for meaningful effects.
So from a scientific viewpoint, there is always uncertainty. Part of the challenge is that too many people on all sides seem to have way too much certainty. It's always best to express in terms of real statistics. In the case of the flu vaccine, the statistics aren't generally great. Between 10-60% effectiveness each year. Most others are much higher.
I agree with everything you said @luckynumber777. Thank you for your comment. I am sure that you know that there are multiple different stains of the flu. So the flu shot is virtually a lottery. There are statistical models that predict which flu strain will be the most common in a year. Personally, I have never gotten a flu shot. And I never gotten the flu. And from what I heard (my mum, the doctors I worked with), the flu shot makes most sense only for people who are at high risk, such as people working in health care, teachers, etc. For everyone else it is not necessary, especially since we do not know which strain of flu may hit you. Again, I really appreciate your input and the fact that you stayed objective and friendly! Cheers!
If it makes you feel good, I have gotten the flu vaccine each of the past 8 years and have had the flu 0 times in that span. The last time I had the flu was 9 years ago :p prior to getting the vaccine.